You can build a killer singlespeed for a lot less money than either of those. I bought a Trek 620 (a mid-'80s touring bike made from Reynolds 531 tubing) for $40, I think it was, at a Salvation Army store. Strip the derailleurs and shifters, pull off the freewheel (the cassette, on newer bikes), remove all the chainrings except the one you want (I kept the middle ring on a 50-36-24 triple), then go to a store that handles BMX bikes and get a one-cog freewheel (a single cassette cog, for a newer bike) with enough spacers to get the chainline straight. In my case, three years or so ago, the freewheel cost $13.95 and the spacers were $1 apiece. I bought three, 1, 2 and 4mm wide, but needed only the 4mm to get a perfect chainline.
There are singlespeed kits available from a number of places, including a freewheel or cog and a handful of spacers. Most sources recommend 2:1 gearing (twice as many teeth in the chainring as in the cog or freewheel) for all-around riding, but you can fudge it either way. You may also need a chain tensioner, but there are ways around that. One source of information is www.sheldonbrown.com, and I think Excel has the kits for $15 or so.

My thinking is build one up if you know what you're doing, and buy one if you don't- can save yourself a lot of headache trying to figure out if Peg A goes in Slot B or what.

One other thing to consider is that most of the fixed-gear people run fairly high gearing on their bikes- around 70 gear-inches or higher. I'm riding a cruiser right now with 52 gear-inches, and that works surprisingly well for certain applications (I've got a coaster brake, which helps with that, too). Try to check around in your area, and see what other people are using. But if the hills kill you, you can gear back quite a bit and still have a rideable bicycle.